reliever vs doer

reliever and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
reliever	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of reliever; that is, doer is a word with a broader meaning than reliever:

reliever: a person who reduces the intensity (e.g., of fears) and calms and pacifies
doer: a person who acts and gets things done

Other hypernyms of reliever include actor, worker.

reliever (noun)	doer (noun)
a pitcher who does not start the game	a person who acts and gets things done
someone who takes the place of another (as when things get dangerous or difficult)
a person who reduces the intensity (e.g., of fears) and calms and pacifies